Tuning T cell properties and functions with biomechanical materials

June 26, 2023

(Nanowerk News) A successful campaign for adoptive T-cell therapy, a type of immunotherapy in which immune T cells are collected from patients, enhanced outside the body, and reinfused into the same patient, especially against blood cancers is ongoing. But increasing the ability to create patient-specific T cell populations with specific traits and functions could broaden the physician’s repertoire of T cell therapies.

One way to approach this goal is to better understand how T cell properties and functions, including their cytotoxic effects on unwanted target cells (effector T cells) or their ability to remember and eliminate them if they arise again (memory T cells), are shaped by resistance. mechanics of the tissues they encounter while infiltrating them.

The mechanical properties of tissues, such as bone, muscle, different internal organs, and blood, can vary widely, and pathological tissues such as tumor masses or fibrotic tissues differ mechanically significantly from healthy tissues.

Now, a research team at the Wyss Institute for Biologically Inspired Engineering at Harvard University and the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS), led by Wyss Core Faculty member David Mooney, Ph.D., is taking a new biomaterials approach to investigate biomaterials. effects of tissue mechanics on the state of T cells.

By engineering a 3-dimensional model of the extracellular matrix (ECM), which is produced by cells responsible for different tissue stiffness and viscoelasticity, they were able to tune the two parameters independently. This enabled them to demonstrate the distinct impact of tissue viscoelasticity on T cell development and function in vitro And lifeand to identify the molecular pathways driving the phenomenon.

The findings are reported in Natural Biomedical Engineering (“Generation of functionally distinct T-cell populations by altering the viscoelasticity of their extracellular matrix”). This cryoEM image shows an ECM mimicking hydrogel with spaces for T cells to pass through and attach to a specially engineered collagen matrix. (Image: Wyss Institute at Harvard University)

Mechanical resistance comes in the form of “stiffness”, the resistance of a tissue (or any material) to instantaneous deformation, and “viscoelasticity”, the type of relaxation it exhibits over time after deformation. Physically explained, viscous (liquid) materials, such as honey, are more likely to flow, while elastic (solid) materials return more quickly to their original shape, such as a rubber band after being stretched – and this is true for tissues consisting of both solid and liquid components.

“Importantly, the phenotype, function, and gene expression program of T cells trained in a variety of systems correlated well with those we found in T cells in tissues that were mechanically different from those of patients with cancer or fibrosis,” said Mooney, who is also Robert P. .Pinkas Family Professor of Bioengineering at SEAS, and leads the Wyss Institute’s Immunomaterials Initiative. “Our study provides a conceptual basis for future strategies aimed at creating functionally distinct populations of T cells for adoption therapy by selectively tuning the mechanical inputs provided by biomaterial-based engineered cell culture systems.”

Mimics grid mechanics on a plate

Key to their discovery was the team’s engineering of a tunable ECM model, in which they focused on the type of collagen they found to be key to dictating the mechanical behavior of different tissues. Collagen is the main ECM protein secreted by almost all cells in the body. Individual collagen protein molecules are naturally organized into crimped fibrils which assemble further into fibers by chemical cross-linking. Each fibril can be thought of as a mechanical spring, and each fiber as an assembly of springs. The stiffness of ECM depends on how densely it is packed with collagen molecules, whereas its different viscoelasticity depends on how tightly the collagen molecules are tightly packed together.

To mimic natural collagen-based ECM, the team created a hydrogel whose stiffness could be adjusted by varying the concentration of collagen molecules: a lower number of collagen molecules results in lower stiffness and a higher number, higher stiffness. Independently, the viscoelasticity becomes manageable by varying the number of synthetic cross-linking molecules that in turn link the collagen molecules. More collagen molecules linked together results in more elastic hydrogel. The resulting ECM mimicking hydrogel equally enables attachment of pre-activated T cells but, importantly, activates their stimulation by specific mechanical signals.

“To our knowledge, this is the first ECM model that allows researchers to study T cells with the rigidity of a viscoelastic separation, and thereby enables us and others in the future to investigate how immune and other cells can be regulated mechanically,” said the co-author of the study. first author Yutong Liu, Ph.D., who is a graduate student in Mooney’s group. “The defined and uniform mechanical stimulation of this system is very different from how T cells are normally cultured – cells attached to the bottom of the culture dish face a highly inelastic surface, while cells remaining in suspension are surrounded by a viscous medium.”

Natural consequence of mechanical action

The team performed extensive analysis of T cells exposed to different viscoelastic conditions. “T cells experiencing a more elastic collagen matrix are more likely to develop into ‘effect-like T cells,’ whereas T cells experiencing a more viscous ECM matrix will become ‘memory-like T cells,’” said first co-author Kwasi Adu-Berchie, Ph. .D., who completed his Ph.D. in Mooney’s lab and is currently a Translational Immunotherapy Scientist at Wyss Institute. “Importantly, we found that the state of T cells, resulting from the viscoelasticity of the matrix, moreover from the more elastic and less viscous hydrogel, becomes imprinted in the long term, as the cells retain memory of that specific matrix after being transferred to a different matrix. This could have far-reaching implications for future cell manufacturing.”

Analysis of gene expression led the team to the activity of a transcription factor known as AP-1 that links T cell acceptance of a more elastic, less condensed mechanical environment to a more effector-like gene expression program. The number of AP-1 complexes with a specific composition increases, and genes that depend on it for expression are enriched, not only in T cells isolated from the more elastic hydrogel, but also in T cells isolated from patient cancer and fibrotic tissue, which are more rigid. and more elastic than the surrounding healthy tissue. When they inhibited one of the AP-1 components with the drug, the effect of the more elastic collagen matrix on T cells was prevented.

To investigate how the different mechanical excitability and predicted gene expression signatures of T cells translate into actual properties and functions, the team used therapeutic CAR-T cells engineered to bind specific antigens from human lymphoma cell lines. Stimulated CAR-T cells in a more elastic collagen matrix in vitro showed a stronger ability to kill lymphoma cells. Also lifeCAR-T cells stimulated in a more elastic matrix, and adoptively transferred to mice with the same type of lymphoma, were significantly more able to reduce tumor burden in animals and prolong their life than CAR-T cells exposed to a less elastic matrix.

“This study combines three seemingly disparate fields, biomaterials, immunotherapy and mechanobiology, to develop an entirely new form of biomaterials-based mechanotherapy. It is easy to see how these findings have the potential to open new avenues for improving adoptable T-cell therapy for patients in the future,” said Wyss Founding Director Donald Ingber, MD, Ph.D., who is also Judah Folkman’s Vascular Professor. Biology at Harvard Medical School and Boston Children’s Hospital, and the Hansjörg Wyss Professor of Bioinspired Engineering at SEAS.

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